Distinct carbon growth mechanisms on the components of Ni/YSZ materials

Abstract

Using pure YSZ and Ni-doped YSZ materials we provide a direct comparison of the morphology and specific growth mechanisms of carbon deposits following treatment in CO as the common component of reformate gas fuels at temperatures up to 1273 K. Under these experimental conditions, carbon is deposited on both constituents following distinctly different pathways: metallic Ni particles are both encapsulated and subsequently act as catalysts for growth of carbon filaments – leading to chemically and electronically altered Ni particles. In contrast to that, also pure YSZ oxide particles are without exception only encapsulated by distorted graphitic layers of up to 2–3 individual layers. This carbon layer is not formed by carbon spillover from the Ni particle, but directly deposited on the oxide grains by CO dissociation. While the pathway over the metallic component is dominant at high Ni loadings, the oxide especially at lower loadings can contribute directly to the structural and chemical alterations of the electrode material by changing the physico-chemical properties, e.g. by altering the conductivity via C-deposition at the intergrain regions or may also serve as additional carbon supply for re-distributed and dispersed “dusted” Ni particles attached to the carbon-covered YSZ grains.